Methods of preparing gas-filled liposomes

Abstract

Methods of and apparatus for preparing gas-filled liposomes are described. Gas-filled liposomes prepared by these methods are particularly useful, for example, in ultrasonic imaging applications and in therapeutic drug delivery systems.

What is claimed is: 
     
       1. A method for preparing gas-filled lipid microspheres comprising shaking an aqueous solution comprising a lipid in the presence of a gas at a temperature below the gel state to liquid crystalline state phase transition temperature of the lipid. 
     
     
       2. A method as in claim 1 wherein the shaking step comprises vortexing. 
     
     
       3. A method as in claim 1 further comprising filtering and heat sterilizing said aqueous lipid solution. 
     
     
       4. A method as in claim 1 further comprising extruding the microspheres through at least one filter of a selected pore size. 
     
     
       5. A method as in claim 4 wherein the pore size is about 10 μm or smaller. 
     
     
       6. A method as in claim 1 further comprising hydrating a dried lipid to form an aqueous solution comprising a lipid. 
     
     
       7. The method of claim 1 wherein said microsphere comprises a lipid selected from the group consisting of dipalmitoylphosphatidylcholine, dipalmitoylphosphatidylethanolamine, and a phosphatidic acid, and said microsphere further comprising polyethylene glycol. 
     
     
       8. The method of claim 1 wherein said lipid comprises at least one dipalmitoyl lipid. 
     
     
       9. The method of claim 1 wherein said lipid comprises dipalmitoylphosphatidylethanolamine and polyethylene glycol. 
     
     
       10. The method of claim 1 wherein said lipid comprises dipalmitoylphosphatidylcholine, phosphatidic acid, dipalmitoylphosphatidylethanolamine, and polyethylene glycol. 
     
     
       11. The method of claim 1 wherein said microsphere comprises a gas selected from the group consisting of a fluorine gas and a nitrogen gas. 
     
     
       12. The method of claim 1 wherein said microsphere comprises a gas which is a fluorine gas. 
     
     
       13. The method of claim 1 wherein said microsphere comprises a gas which is nitrogen. 
     
     
       14. The method of claim 1 wherein said microsphere comprises a gas selected from the group consisting of a fluorine gas and a nitrogen gas and a lipid selected from the group consisting of dipalmitoylphosphatidylcholine, dipalmitoylphosphatidylethanolamine, and a phosphatidic acid, and said microsphere further comprising polyethylene glycol. 
     
     
       15. The method of claim 1 wherein said microsphere comprises a gas selected from the group consisting of a fluorine gas and a nitrogen gas and a lipid comprising dipalmitoylphosphatidylcholine, phosphatidic acid, dipalmitoylphosphatidylethanolamine, and polyethylene glycol. 
     
     
       16. The method of claim 1 wherein said microsphere comprises a gas which is a fluorine gas and a lipid comprising dipalmitoylphosphatidylethanolamine and polyethylene glycol. 
     
     
       17. The method of claim 1 wherein said microsphere comprises 90% gas. 
     
     
       18. The method of claim 1 wherein said microsphere comprises a gas which is a fluorine gas and a lipid comprising dipalmitoylphosphatidylethanolamine and polyethylene glycol, said microsphere comprising 90% gas. 
     
     
       19. The method of claim 1 performed at a pressure above ambient pressure.